We've used reusable swim diapers for all of our kids. We tried the disposable ones one time on a vacation and hated them. They don't work! There is no elastic around the waste so that means the poop just floats away into the pool/lake/ocean/whatever. Eww! Most public and neighbhorhood pools around here won't even allow disposable swim diapers for this reason. They only allow swim diapers that have elastic around the legs and the waist.
I haven't tried the ones from One Step Ahead. We've gotten ours from places like Meijer and Target in the kid pool/summer toy areas (where the goggles, snorkels, floaties, water guns, etc are). They come in several sizes and lots of different designs and are only a few bucks.